The detection of pathogenic bacteria remains a challenge for the struggle against biological weapons, nosocomial diseases, and for food safety. In this research, our aim was to develop an easy-to-use electrochemical immunosensor for the detection of pathogenic Staphylococcus aureus ATCC25923. The biosensor was elaborated by the immobilization of anti-S. aureus antibodies using a self-assembled monolayer (SAMs) of 3-Mercaptopropionic acid (MPA). These molecular assemblies were spontaneously formed by the immersion of the substrate in an organic solvent containing the SAMs that can covalently bond to the gold surface. The functionalization of the immunosensor was characterized using two electrochemical techniques: cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Here, the analysis was performed in phosphate buffer with ferro/ferricyanide as the redox probe. The EIS technique was used for affinity assays: antibody-cell binding. A linear relationship between the increment in the electron transfer resistance (R_CT) and the logarithmic value of S. aureus concentration was observed between 10 and 10⁶ CFU/mL. The limit of detection (LOD) was observed at 10 CFU/mL, and the reproducibility was calculated to 8%. Finally, a good selectivity versus E. coli and S. epidermidis was obtained for our developed immunosensor demonstrating its specificity towards only S. aureus.

A DNA biosensor based on a modified gold electrode with a Au/cysteine/DNA matrix was developed for ultratrace determination of genotoxicity antibiotics. The modified Au/cysteine/DNA electrode was characterized by cyclic voltammetry and impedance spectroscopy methods. The interaction between immobilized DNA and genotoxicity antibiotics in hospital wastewater was investigated using differential pulse voltammetry (DPV) technology. Using this technique, ciprofloxacin and ofloxacin were detected in real time in the hospital wastewater (HW) of the Tunisian cities of Gabes, Tozeur, Sfax, and Gbeli. In addition, physicochemical parameters such as the chemical oxygen demand (COD), biological oxygen demand (BOD), and total organic carbon (TOC) of HW samples that may affect the nature of the samples were studied. Comet assay (single-cell gel electrophoresis) was performed to measure the capacity of xenobiotics to induce DNA damage. In our conditions, this test indicated that all tested wastewater was able to alter cell integrity and cause DNA molecular damage, and the most genotoxic effect was found in the wastewater of Gabes hospital. Results show that the concentrations of the two antibiotics reached 33 and 40 ng/mL in the hospital wastewater of Gabes and Tozeur, respectively. The DNA biosensor based on the modified gold electrode exhibited superb performance and offers a probable application for the detection of genotoxicity antibiotics in hospital wastewater. The level of genotoxicity is proportional to the concentration of antibiotics detected in hospital wastewater. We will explore the application of this model for continuous monitoring downstream of hospital discharge and wastewater treatment plants for effective control of the presence of genotoxic products.

This study investigated the adaptive mechanisms of Shigella sonnei ATCC25931 in response to gamma irradiation stress (0.5 and 1 kGy), with a specific focus on the involvement of fatty acids (FAs) in membrane lipid composition remodeling, adherence, and extracellular proteins. The results demonstrated a notable enhancement in cell hydrophobicity and adherence to KB cells following irradiation, although the invasion rate exhibited a decline from 14% to 2.35% at 1 kGy. Furthermore, gamma irradiation induced notable alterations in fatty acid (FA) composition, characterized by a pronounced reduction in the unsaturated/saturated FA ratio. Additionally, the plasmid profiles revealed the loss of several original plasmids after gamma irradiation. The alterations in extracellular proteins were observed through SDS-PAGE, which demonstrated a reduction in expression at 1 kGy. Furthermore, a molecular docking analysis indicated that fatty acids play a role in inhibiting VirF, a key regulator of Shigella virulence. The least effective inhibitor was capric acid, while linoleic and gamma-linolenic acids formed the most stable inhibitory complexes, which prevented VirF from activating the virulence system. These alterations in fatty acids, plasmids, and extracellular proteins constitute adaptive responses to irradiation-induced stress.